The present invention relates to hydrojet surgical devices, and more particularly to hydrojet devices used for refractive surgery.
In recent years the use of surgical techniques for correction of ophthalmic refractive malfunction has progressed from experimental laboratory operations to widely accepted, commonplace procedures. Radial keratotomy (RK), photorefractive keratotomy (PRK), and myopic keratomileusis (MKM) have all become routine techniques in ophthalmology. Such aggressive surgical treatment is a relatively new development in ophthalmology. However, many patients require good uncorrected visual acuity for various occupations, such as pilots or professional athletes, and other patients demand good uncorrected visual acuity for cosmetic or psychological reasons. Moreover, some patients have subnormal vision, even when optimally corrected with spectacles or contact lenses, and seek surgical correction for improved vision.
Some photorefractive surgical techniques involve a lamellar keratotomy, in which a hinged flap of apical corneal tissue is created by incision in the cornea generally perpendicular to the primary visual axis. A second cut is then made, in which a thin wafer of stroma is removed. The flap is then returned to its initial position and permitted to heal in place. Removal of the thin wafer of stroma alters the conformation of the corneal apex, thereby modifying the refractive characteristic of the cornea. Clearly, the placement and formation of the second cut, as well as the thickness and planarity of the first incision, are crucial to the success of this technique.
Lamellar keratotomy has been performed using a microkeratome device, in which a high speed rotating cutting head supports a blade that creates the corneal cuts. However, the blade thickness, as well as the mechanical vibration and motion of the moving cutter limits the fineness and planarity of the incisions, which in turn limits the potential for successful outcome of the surgery.
Recently, a high speed water jet has been used in lamellar keratotomy, in a technique termed hydrorefractive keratoplasty (HRK). A water jet having a diameter of 50-100 .mu.m is used to form the corneal incisions. The water jet is far smaller in diameter than the thickness of a cutting blade, whereby the incisions may be much finer, resulting in less tissue trauma, better healing, and greater potential for success. The water jet is a linear "beam" which must be swept through the corneal tissue to effect the necessary incisions. The mechanism to effect the beam movement consists generally of a track on which the water jet nozzle is mounted in slidable fashion. However, it is recognized in mechanical engineering that two slidable surfaces must have a clearance of approximately .+-.0.001 inch, equal to 25.4 .mu.m. Thus the free play of the sliding mechanism is 25%-50% of the cutting beam diameter, which substantially negates the advantages of using a hydrojet as a fine cutting instrument. The prior art demonstrates a need for an improved mechanism for guiding a hydrojet cutting beam with greater resolution and control.